It has been generally performed in past in order to still more cope with downsizing and high functionality of an electronic component such as a cellular phone and a digital camera that a package has bumps (bump electrodes) formed by solder balls or solder paste on its elementary surface and any reflow processing then performed to a printed circuit board enables the package to be bonded to the printed circuit board.
A composition of plating used for electrodes of the package and a composition of plating used for electrodes of the printed circuit board have been determined by taking into consideration any reasons of design and any costs. Accordingly, the composition of plating used for the electrodes of the package and the composition of plating used for the electrodes of the printed circuit board may be different from each other. For example, there has been a case where a package having an electrode on which Ni/Au is plated is bonded to the printed circuit board having a Cu electrode or an electrode on which Cu is plated (hereinafter, merely referred to as “Cu electrode”) using an alloy of Sn—Ag—Cu series (as one example thereof, Sn-3.0Ag-0.5Cu, hereinafter, briefly referred to as “SAC alloy”) now generally used as Pb-free solder, or a case where a package having an electrode on which Ag—Pd alloy is plated is bonded to the printed circuit board having the Cu electrode using the SAC alloy. As the composition of plating other than those, Ag, Ni, and Ni—P have been also known.
Optimization of the composition of solder alloy, flux, soldering condition and the like, respectively has been known as a conventional way to improve any solderability and/or bonding strength thereof. In addition, a way to consider a composition of plating on an electrode to be soldered has also been known. Patent documents 1 and 2 disclose an invention to consider a composition of plating on an electrode, particularly an electrode on which electroless Ni plating is performed.